Method for operating a refuse incineration plant

ABSTRACT

The invention relates to a method for operating a refuse incineration plant and to a regulating system, in which, after the fire has been fanned, the generation of heat is made more uniform by regulating at least one of the operating parameters refuse metering, residence time on a grate, quantitative supply of primary air and quantitative preheating of primary air. To match the operating parameters to a varying calorific value of the refuse, the calorific value of the refuse is recorded as well as the standard regulating variables and is used to adapt the regulating means. The measure used for the calorific value is, for example, the moisture content of the flue gas generated during the incineration. Consequently, there is no need for the operator to estimate the calorific value and manually adapt the operating parameters accordingly.

[0001] The invention relates to a method for operating a refuseincineration plant as claimed in the preamble of claim 1, to aregulating system for regulating at least one of the operatingparameters of a refuse incineration plant as claimed in claim 10, and toa refuse incineration plant having a regulating system of this type.

[0002] The operation and in particular the uniform generation of heat inoil-fired or coal-fired power plants does not cause problems. Thisuniform generation of heat is achieved by uniform metering of the fuel,the quality of which is constant and known. The main aim of refuseincineration plants too is to keep the heat output constant. Inaddition, the flue gas has to comply with certain statutory regulationswith regard to quality and quantity. The heat output cannot becontrolled simply by metering the refuse supplied, since the calorificvalue of the refuse, on account of its differing composition and thevarying water content, may fluctuate considerably. Accordingly, it isalready difficult to maintain a constant quantity of heat. Additionaloptimization of the other parameters causes even more problems.

[0003] EP-B-0 499 976 has disclosed a method for operating a refuseincineration plant in which, to make the amount of heat which isgenerated more uniform, the supply of refuse, i.e. the movement of themetering ram, the conveying of refuse on the grate, i.e. movement orlifting frequency of the grate parts, and the supply of primary air isregulated by means of a cascaded regulating system. The quantity ofsteam which is generated is recorded with a slight delay and is used asthe main regulating variable. The value for the oxygen content of theflue gas, which is rapidly available, is used as an auxiliary regulatingvariable. With this firing capacity regulation, it is possible for therefuse incineration plant to be substantially automatically matched toslightly changing properties of refuse and therefore to minorfluctuations in calorific value. However, the grate frequency, rammovement and primary air supply are always increased or reduced in thesame direction. Consequently, this fire capacity regulation does notsufficiently compensate for relatively substantial changes in thecondition or calorific value of the refuse which require the operatingparameters to be changed in opposite directions. This is the case, forexample, when switching over to wet, highly compacted refuse, in whichcase the ram velocity should be lowered in order to reduce the supply ofrefuse and the grate frequency should be increased in order to split orbreak up the refuse. In the known process, although the fluctuation incalorific value is compensated for in the short term by fanning orretarding the firing intensity and in the longer term by means of themetered quantity of refuse, the automatic fire capacity regulation takesno account of the correct incineration profile over the grate length.

[0004] In practice, such changes in the calorific value are usuallycompensated for by an operator by visual assessment of the condition ofthe refuse or the state of the fire. The operator then manually adjustsindividual operating parameters; for example, in the case of wet refuse,the primary air preheating is often increased. A problem of this is thatit is complicated to adjust the operating parameters, on account of thewide range of possible actions and interactions, and the adjustments arenot always selected optimally. Furthermore, success is very dependent onthe experience of the operator. The regulating process has an extremelylong delay time, and consequently the full effects of an interventioncan only be assessed after about an hour.

[0005] Therefore, the invention is based on the object of simplifyingoperation of a refuse incineration plant, in particular of providing amethod for operating a refuse incineration plant in which the operatingparameters are to a large extent automatically adapted to changingrefuse properties, in particular fluctuations in the calorific value.

[0006] The object is achieved by a method for operating a refuseincineration plant having the features of claim 1. The object is alsoachieved by a regulating system having the features of claim 10 and arefuse incineration plant using such a regulating system having thefeatures of claim 15.

[0007] Advantageous refinements of the invention will emerge from thedependent claims, the description and the drawings.

[0008] To operate a refuse incineration plant, after the fire has beenfanned, the generation of heat is made more uniform (fire capacityregulation) in a manner known per se by regulating a plurality ofoperating parameters, including at least one of the operating parametersrefuse metering, residence time on a grate and quantitative supply ofprimary air, as a function of a plurality of measured variables,including at least one of the measured variables oxygen content in theflue gas and quantity of steam generated. By way of example, the methodwhich is known from EP-B 0 499 976 is used. According to the invention,a calorific value parameter, which is a measure of the calorific valueof the metered refuse or the change in this value, is derived from ameasured variable. As a modification to the known control techniques, atleast one of the operating parameters is adjusted at least in part as afunction of the calorific value parameter.

[0009] The calorific value or the change in this value is automaticallyrecorded by analyzing suitable measured variables. The calorific valueparameter is used to influence the regulation of at least one operatingparameter in accordance with a predetermined plan which is, for example,empirically determined or drawn up using model calculations. Ideally,therefore, no manual intervention is required, but rather theintervention takes place automatically on the basis of objectivecriteria, and the plant can in principle be left to run itself.

[0010] In addition, it is also possible to provide the option of manualintervention. To this end, the calorific value or the change in thisvalue is estimated by an operator, for example by observing the fireposition. The process control unit is used to input as calorific valueparameter a variable which indicates, for example, the extent to whichthe estimated calorific value deviates from the nominal calorific valueassumed when dimensioning the firing installation.

[0011] The measured variable for the calorific value parameter isrecorded automatically. In an advantageous refinement of the method, themoisture content of the flue gas is used as a measure for the calorificvalue. This is based on the fact that the calorific value of the refuseis substantially determined by its water content. Since the watercontained in the refuse begins to evaporate as soon as it is fed intothe furnace, the measured moisture content reproduces changes in therefuse composition without a major time delay. A corresponding signal isthen immediately available in order for the operating parameters or theregulation thereof to be matched to the changed calorific value. Themoisture content of the flue gas can be measured directly by means of ahumidity sensor. Preferably, however, the flue gas is saturated withwater, and the readily measurable temperature of the saturated flue gasis used as a measure of the moisture content and therefore of thecalorific value. The extraction of heat through evaporation is greaterif less water was present in the flue gas from the outset. Thetemperature of the water-enriched flue gas is therefore a measure of theoriginal water content of the refuse and therefore of the calorificvalue. Since in many refuse incineration plants a water injection meansand a scrubber are present, this variant can be implemented particularlyeasily. The temperature is preferably measured downstream of the waterinjection means, in the sump of the scrubber or at the scrubber outlet.

[0012] The calorific value parameter is used to automatically determineat least one correction variable which modifies at least one of thesetting values from the fire capacity regulation and/or one of thevariables used for fire capacity regulation, e.g. input variables oramplifications of regulators involved. Preferably, a plurality ofoperating parameters are influenced in such a way, so that, by means ofan intervention or on the basis of the automatically recorded calorificvalue, the characteristic diagram of the entire plant can be shifted andoptimally matched to the changed calorific value. Correction variablesare determined, for example, on the basis of model calculations or arebased on empirical values.

[0013] The correction variable is used, for example, to shift thesetting range or working point of an individual regulator, while thecapacity regulation otherwise keeps the heat output constant in a knownway.

[0014] In a further advantageous refinement of the invention, thecorrection variable determined from the calorific parameter value isused to modify the regulator amplification of at least one regulator. Inthis way, the operating range of this regulator is adapted to thechanged calorific value. In addition, corresponding correction variablesdetermined from the same calorific value parameter can also be used toadapt the setting value and/or the desired value of this regulator or ofother regulators.

[0015] Preferably, the following operating parameters are adjusted as afunction of the calorific value parameter: sum of primary air andsecondary air, ratio of primary air to secondary air, zone flapposition, primary air, refuse metering, residence time on the grate,desired oxygen value, primary air preheating.

[0016] The regulating system according to the invention for regulatingat least one of the operating parameters of a refuse incineration planthas at least one regulator which, on the basis of at least oneregulating variable supplied as input signal and/or at least one desiredvalue, generates an output signal which is fed as setting value to oneof the actuators ram, grate, primary air flaps or primary air preheater.According to the invention, there is a first measuring device forrecording a measured variable from which a calorific value parameter,which is a measure of the calorific value of the refuse or the change inthis value, is derived. Furthermore, there is a calorific valuecorrection unit which, on the basis of the calorific value parameter,generates at least one correction variable, which is used to modify atleast one desired value and/or setting value and/or a regulatoramplification of the at least one regulator.

[0017] The regulating system is used in particular to carry out themethod according to the invention.

[0018] A refuse incineration plant having a regulating system of thistype has all the advantages of the regulating system.

[0019] Exemplary embodiments of the invention are illustrated in thefigures and described below. In the figures:

[0020]FIG. 1 diagrammatically depicts a flow diagram of a refuseincineration plant;

[0021]FIG. 2 diagrammatically depicts an example of a regulating meansaccording to the invention;

[0022]FIG. 3a diagrammatically depicts examples for characteristiccurves of a servo regulator for the grate at different calorific values;

[0023]FIG. 3b diagrammatically depicts examples for characteristiccurves of a servo regulator for the air supply at different calorificvalues;

[0024]FIG. 4 diagrammatically depicts an example of a regulator circuitfor the servo regulator.

[0025]FIG. 1 shows a flow diagram of a refuse incineration plant. Refuseis fed to the combustion chamber 101 by means of a ram (not shown here).The refuse which is metered in passes onto a driven incineration grate(not shown here), where it is dried, degassed and incinerated. Theincineration sequence is influenced by the supply of primary air,secondary air and the grate movement. The hot flue gases 102 pass fromthe combustion chamber 101 into a boiler (not shown here), where theyare used for steam generation. The flue gas then passes through a waterinjection means or quench device 103, in which the flue gas 102 issaturated with water 104. The saturated flue gas 105 is then fed to theflue-gas cleaning stage 106.

[0026] A temperature-measuring device 108 measures the temperature ofthe water-saturated flue gas 105. The measured value is fed to aprocessing unit 109, which generates a calorific value parameter 110.The processing unit 109 comprises, for example, a PI regulator. By wayof example, the deviation of the instantaneous temperature of thesliding temperature mean is taken as a measure of the calorific value orthe calorific value deviation. The temperature of the flue gas which isused for regulation purposes may be measured downstream of the quenchdevice 103, in the sump of the scrubber 106 or in the region of thescrubber outlet.

[0027] To determine the calorific value parameter 110, it is alsopossible to measure the moisture content of the unsaturated flue gas 102using a humidity-measuring device 107 and for this measurement to beevaluated in the processing unit 109. This is recommended in particularfor plants without a quench device 103.

[0028] In a manner which is known per se, the regulating system shown inFIG. 2 has measuring devices 201, 202 for measuring the oxygen contentof the flue gas and the quantity of steam. The operating parameters areregulated as follows: refuse metering by influencing the actuator “ram”209, residence time on the grate by influencing the actuator “grate”210, primary air preheating by influencing the corresponding actuator208 and further parameters of the primary and secondary air supply anddistribution by influencing the functional unit “air” 211, which mayinclude further regulators. The functional unit “air” 211 is used toinfluence, for example, actuators which are not shown here for the totalair quantity, primary air quantity, secondary air quantity, air supplyto the individual grate zones.

[0029] The measured value for the quantity of steam 222 is fed as inputsignal to a main or lead regulator 203. This is preferably aslow-operation PI regulator. Its output signal 223 is fed to threedownstream auxiliary or servo regulators 204, 205, 206, which arepreferably quick-operation P regulators. The desired value of theauxiliary regulators 204, 205, 206 is adjusted by the output signal 223of the main regulator 203 on the basis of the measured steam values. Themeasured value for the oxygen content 224 is fed to the auxiliaryregulators 204, 205, 206 as a further input signal. The predetermineddesired value for the oxygen content 213 is used as a third input signalfor all three auxiliary regulators 204, 205, 206. The outputs of theauxiliary regulators 204, 205, 206 are connected to the actuators ram,grate and air 209, 210, 211.

[0030] A control unit 214 is used to determine the basic setting of theactuators 209, 210, 211 on the basis of a predetermined desired steamvalue 212. Corresponding signals 226 are fed to the actuators 209, 210,211 as basic setting values. These basic setting values are modified bythe output signals from the auxiliary regulators 204, 205, 206, whichare added, for example, to the basic setting values 226.

[0031] According to the invention, the control system which has beendescribed hitherto and is known per se is expanded by a feature allowingthe regulation to be automatically adapted to changing calorific values.For this purpose, there is a measuring device 217 for providing ameasured variable from which a measure of the calorific value or itschange can be derived, for example the temperature of thewater-saturated flue gas. A calorific value parameter 228, which is fedas input variable to a calorific value correction unit 215, is generatedfrom this measured variable in a unit 216. This correction unit uses thecalorific value parameter to determine a plurality of correctionvariables 218, 219, 220, 221, which are used to modify the regulation ofthe operating parameters. Firstly, the calorific value correction unit215 generates an oxygen desired-value correction variable 218, which isused to match the oxygen desired value 213 fed to the auxiliaryregulators as input variable 225 to the changed calorific value, forexample by adding the correction variable to the desired value.Setting-value correction variables 219 are used to modify the settingvalue 227 fed to the actuators 209, 210, 211. By way of example, thesetting value 227 used is the sum of the output signal from theauxiliary regulators 204, 205, 206, the corresponding basic settingvalue 226 and the corresponding correction variable 226. By suitablyassigning correction variables 226 to the individual actuators, it ispossible, by means of a single, automatically executed intervention, tooptimally match the operating parameters to the current calorific value.By way of example, in the event of a transition to wet, highly compactedrefuse (lower calorific value), the ram velocity is reduced (negativecorrection variable for actuator ram 209) and the grate liftingfrequency is increased (positive correction variable for actuator grate210).

[0032] In a preferred refinement of the invention, the calorific valuecorrection unit 215 generates further correction variables 220, whichare used to modify the amplification of the auxiliary regulators 204,205, 206. By way of example, at high calorific values the amplificationof the auxiliary regulator 205 which regulates the actuator grate 210 isincreased and the amplification of the auxiliary regulator 206 whichregulates the functional unit air 211 is reduced. At the same time, thebasic setting values are adapted using correction variables 219. This isbased on the discovery that different refuse calorific values requiredifferent regulator responses (amplifications) for the same regulatordeviation. Furthermore, the burn-off behavior of the refuse on the grateis dependent on the calorific value and therefore requires measureswhich ensure the optimum grate coverage for any condition of refuse(adaptation of the basic setting values). By way of example, at highcalorific values the plant is preferably operated with a grate bias,i.e. with a short residence time on the grate, and at low calorificvalues the plant is preferably operated with an air bias. This can beachieved by modifying the regulator amplification in accordance with theinvention.

[0033] The calorific value correction unit 215 generates a furthercontrol variable 221 which serves directly as a setting value for theprimary air preheating actuator 208.

[0034]FIGS. 3a and 3 b in each case show two examples of characteristiccurves of a servo regulator for the grate and for the air supply and thesetting variables of the corresponding actuators for high calorificvalues (dashed line) and low calorific values (dotted line). FIG. 3ashows the grate lifting frequency f_(R) as a function of the measuredoxygen content or the deviation of the servo regulator. If the controldeviation is zero, the setting value x1, x2 is given by the basicvariable which has been determined by the control unit 214 and correctedon the basis of the recorded calorific value. Accordingly, the basicsetting x1 for a high calorific value is lower than the basic setting x2for a low calorific value. The increase in the characteristic curves isdetermined by the regulator amplification, which is higher for a highcalorific value than for a low calorific value. In the case of theprimary air supply PL, the regulation of which is illustrated in FIG.3b, the basic setting X1, X2 and regulator amplification are lower for ahigh calorific value than for a low calorific value.

[0035]FIG. 4 shows an example of a regulator circuit for the servoregulators 205 or 206 from FIG. 2. Correction variables 218, 219, 220are generated from the calorific value parameter 228 in the calorificvalue correction unit 215. The association takes place on the basis ofpredetermined functions, which are symbolized in FIG. 4 by nonlinearcurves in the unit 215. The oxygen desired value 213, with the outputsignal 223 from the steam regulator, which indicates the oxygen desiredvalue shift, and the desired value correction variable 218, is fed to anadder. The difference with respect to the current oxygen measured value224 is amplified or attenuated, the proportionality factor beingdetermined by the regulator amplification correction variable 220. Thebasic variable 226 for the setting value 227 and a setting-valuecorrection variable 219 is added to this regulator amplificationcorrection variable 220. The basic variable 226 for the setting value227 is generated in the control unit 214 by multiplication and additionusing predetermined variables from the preset steam desired value 212.The actuator 209 or 210 is actuated using the setting value 227generated in this way.

1. A method for operating a refuse incineration plant, in which, afterthe fire has been fanned, the generation of heat is made more uniform byregulating a plurality of operating parameters, including at least oneof the operating parameters refuse metering, residence time on a grateand quantitative supply of primary air, as a function of a plurality ofmeasured variables, including at least one of the measured variablesoxygen content in the flue gas (224) and quantity of steam generated(222), wherein a calorific value parameter (228), which is a measure ofthe calorific value of the refuse or the change in this value, isgenerated from a further measured variable, and at least one of theoperating parameters is adjusted at least partially as a function of thecalorific value parameter (228).
 2. The method as claimed in claim 1,wherein at least two, and preferably all, of the following operatingparameters are adjusted as a function of the calorific value parameter(228): sum of primary air and secondary air, ratio of primary air tosecondary air, zone flap position, quantity of primary air, refusemetering, residence time on the grate, desired oxygen value, primary airpreheating.
 3. The method as claimed in claim 1 or 2, wherein thecalorific value parameter (228) is determined from the moisture contentof the flue gas (102) which is generated during the incineration.
 4. Themethod as claimed in claim 1, 2 or 3, wherein the calorific valueparameter (228) is determined from the temperature of the flue gas (104)which is generated during the incineration and is then saturated withsteam.
 5. The method as claimed in one of the preceding claims,characterized in that at least one correction variable (218, 219, 220,221) is assigned to the calorific value parameter(228) or is assignedaccording to a predetermined rule, and this correction variable is usedto modify at least one input variable (desired value) (225) and/or atleast one output variable (setting value) (227) of at least oneregulator (204, 205, 206) which is used, in a manner known per se, toadjust or regulate the at least one operating parameter.
 6. The methodas claimed in claim 5, wherein the sum of the output variable of aregulator (204, 205, 206), a correction variable (219) generated on thebasis of the calorific value parameter (228) and preferably apredetermined basic setting value (226) is used to adjust an operatingparameter.
 7. The method as claimed in claim 5 or 6, characterized inthat a correction variable (218) is used to modify the input variable(desired value) (225) for a regulator (204, 205, 206).
 8. The method asclaimed in one of the preceding claims, wherein at least one correctionvariable (219) is assigned to the calorific value parameter (228) or isassigned according to a predetermined rule, and this correction variableis used to modify at least the regulator amplification of at least oneregulator (204, 205, 206) which is used, in a manner known per se, toadjust or regulate the at least one operating parameter.
 9. The methodas claimed in one of the preceding claims, wherein, to regulate theoperating parameters, refuse metering, residence time on a grate,quantitative supply of primary air and primary air preheating, settingvalues (227) which are derived from at least the measured variablesoxygen content in the flue gas (224) and quantity of steam generated(222) and are modified as a function of the calorific value parameter(228) are used.
 10. A regulating system for regulating at least one ofthe operating parameters of a refuse incineration plant, having at leastone regulator (203, 204, 205, 206) for regulating at least one of theactuators ram (209), grate (210), primary air flaps (211) or primary airquantity preheater (208), which system has a measuring device (107, 108,217) for recording a measured variable, from which a calorific valueparameter (228), which is a measure of the calorific value of the refuseor the change in this value, is derived, and a calorific valuecorrection unit (215) which, on the basis of the calorific valueparameter (228), generates at least one correction variable (218, 219,220, 221), which is used to modify at least one input variable (225)and/or an output variable (227) and/or a regulator amplification of theat least one regulator (203, 204, 205, 206).
 11. The regulating systemas claimed in claim 10, wherein the measuring device (107, 108, 217)records the moisture content of the flue gas (102) or the temperature ofthe water-saturated flue gas (104).
 12. The regulating system as claimedin claim 10 or 11, characterized in that the calorific value correctionunit (215) has a circuit which is used to assign a plurality ofcorrection variables (218, 219, 220, 221) to the calorific valueparameter (228), preferably a processor which is used to calculate thecorrection variables (218, 219, 220, 221) from the calorific valueparameter (228).
 13. The regulating system as claimed in one of claims10 to 12, characterized in that measuring devices for measuring thequantity of steam and the oxygen content (202; 201) of the flue gas arepresent.
 14. The regulating system as claimed in claim 13, which has amultiloop regulating device having a main regulator (203), to which amain regulating variable derived from the measured quantity of steam(222) is fed, and at least three quicker auxiliary regulators (204, 205,206) which are connected downstream of the main regulator (203), whichare fed an auxiliary regulating variable derived from the measuredoxygen content (224) and the outputs of which are in each case connectedto one of the actuators (209, 210, 211), the correction variables (218,219, 220, 221) being used to modify an input variable and/or an outputvariable and/or a regulator amplification of at least one of theauxiliary regulators (204, 205, 206), preferably of all the auxiliaryregulators (204, 205, 206).
 15. A garbage incineration plant having acombustion chamber, which has a grate, a boiler and having theregulating system as claimed in one of claims 10 to
 14. 16. The refuseincineration plant as claimed in claim 15, having a water injectionmeans (103) for saturating the flue gas generated during the refuseincineration with steam, and having a measuring device (108) formeasuring the temperature of the steam-saturated flue gas (105), whichis arranged downstream of the water injection means (108).
 17. Therefuse incineration plant as claimed in claim 15, having a measuringdevice for measuring the moisture content of the flue gas.